Temperature control is the primary concern during the design and construction process of mass concrete structures. As the concrete production has an enormous negative environmental impact, the development of green mass concretes will eventually become as important as the thermal characteristics. Therefore, this paper investigates the use of Electric Arc Furnace (EAF) steel slag aggregate for the partial replacement of the natural aggregate in the production of mass concrete. The impact of EAF steel aggregate on mass concrete workability, strength, and thermal behaviour was analysed. In addition, a cradle-to-gate LCA study was conducted to evaluate the environmental footprint and sustainability potential of the tested mass concrete mixtures. The study results suggest that the use of EAF steel slag aggregate in combination with a low-heat cement with a high content of blast furnace slag can significantly lower the temperature, reduce the environmental impact, and increase the sustainability potential of mass concrete, while at the same time providing sufficient workability and compressive strength. The study results indicate that EAF steel slag can be upcycled into an aggregate for the production of green mass concrete mixtures.